The present invention relates to an arrangement for the control of the power transmission of an all-wheel drive vehicle, having a main driving axle equipped with the transverse differential, and an auxiliary driving axle that is driven by a longitudinal clutch that is continuously controllable. The longitudinal clutch is continuously controlled by a control element and a control unit which receives inPut signals from a plurality of sensors and generates a control quantity for the control of the control element of the longitudinal clutch. The control quantity is determined as a function of at least one traction force of the wheels, this traction force being determined by the control unit as a function of a desired traction force and a distribution factor that is determined from at least one of the desired traction force and at least one of the input signals according to a characteristic diagram.
According to commonly-owned U.S. Pat. application Ser. No. 787,439, filed Oct. 15, 1985, an arrangement for the control of the power transmission of a four-wheel drive vehicle is provided that achieves, with a relatively small number of sensor-acquired operating and driving parameters and low control expenditures, the traction advantages of four-wheel drive combined with the advantages of the vehicle handling of two-wheel drive. This is achieved without the respective disadvantages of four-wheel and two-wheel drives.
This is primarily achieved in that commonly-owned application by determining a proportion Fzf of the traction force of the wheels at the auxiliary driving axle from an amount of a desired traction force (Fzs) that is multiplied with a distribution factor. This amount of desired traction force (Fzs) is determined from a desired performance Ps (as desired by the driver) and a vehicle speed vf. The distribution factor in this case is determined from the amount of the desired traction force (Fzs).
It is an objective of the present invention to provide an arrangement for the control of the power transmission onto the wheels of a four-wheel drive vehicle that further improves the overall driving-dynamic handling of a motor vehicle that can be achieved by the arrangment according to commonly-owned Application Ser. No. 787,439 and that particularly reacts to disturbances in a more refined way.
This and other objectives are achieved by preferred embodiments of the present invention which provide an arrangement for controlling the power transmission to the axles on an all-wheel driven motor vehicle that has a longitudinal clutch which is continuously controllable by a control unit which generates a control quantity for the control of longitudinal clutch as a function of at least one traction force of the wheels, said traction force being determined as a function of a desired traction force and a distribution factor. This distribution factor is determined from at least one of the desired traction force and at least one of the input signals according to a first characteristic diagram. The arrangement includes means for determining a driving resistance from a vehicle driving speed; a means for determining an excess traction force as a difference of the amount of the desired traction force and the driving resistance. The distribution factor is obtained at least from the amount of the excess traction force according to the first characteristic diagram 39.
In another preferred embodiment of the present invention, the arrangement is provided with means for determining a time-related change of the vehicle speed and means for determining the distribution factor from at least this time-related vehicle speed change according to the first characteristic diagram 39.
Some of the advantages of the invention are that the driving-dynamic overall handling of the motor vehicle is further improved because the arrrangement and therefore the whole vehicle system adapts itself better to inner disturbances (such as load changes) and to outer disturbances (such as abruptly changing conditions affecting the coefficient of friction in the contact between the wheel and the road).
This is achieved by determining the distribution factor df via a characteristic diagram from an excess traction force. This excess traction force is calculated by forming the difference between the amount of the desired traction force (Fzs) and a driving resistance Fv that is determined via a characteristic driving resistance curve from the vehicle speed vf.